\section{Similar Solutions and Tools}
A wide array of software tools exist that can be used when learning about sound. To have a frame of reference it was chosen to research the market for existing tools that try to solve the same problems as this project. The following will describe some of the programs that were found during the initial phase of the project.

\textit{Train Your Ears EQ Edition} is a training tool with the goal of making people better at recognizing equalized filters. It starts by playing an unaltered piece of music. Then a random equalizer filter is applied to the signal. Now the user has to estimate what parameters have been used to alter the signal. After each guess, the user can hear, observe and compare the two signals (see figure \ref{fig:trainYourEars}), and thereby, learn about the effects of an equalizer. According to the developers behind the program, doing this repeatedly for various sound signals will increase one's awareness and understanding of how an equalized signal sounds.

\begin{figure}[htbp]
\centering
\includegraphics[width=0.8\textwidth]{images/SimilarTools/trainYourEars}
\caption{Train Your Ears is used to learn about sound equalizers \cite{trainYourEars}.}
\label{fig:trainYourEars}
\end{figure}

\textit{Audio Tool} is a tool for measuring  sound level, and helps the user to keep rhythm and tempo. One feature is called the "Audio Atlas", which is a dictionary with definitions of the most commonly-used audio terms, as shown in figure \ref{fig:audioTool_Atlas}.

\begin{figure}[htbp]
\centering
\includegraphics[width=0.3\textwidth]{images/SimilarTools/audiotool_Atlas.jpg}
\caption{Audio Tool provides a dictionary with useful terms and definitions \cite{audioToolAtlas}.}
\label{fig:audioTool_Atlas}
\end{figure}

Whereas \textit{Train Your Ears EQ Edition} and \textit{Audio Tool} are for training the user's knowledge about sound topics and equalizers, there is a plethora of sound visualizers that can be found on the Internet. To name but a few, there are \textit{Sound Visualizer} (see figure \ref{fig:soundVisualizer}), \textit{Sound Vizz} (see figure \ref{fig:soundVizz}) and \textit{AudioTools} (see figure \ref{fig:audioTools}). However, these apps are mostly just for pure visualization without trying to teach anything about the sound signals.

\begin{figure}[htbp] \centering
\begin{minipage}[b]{0.45\textwidth} \centering
\includegraphics[width=0.70\textwidth]{images/SimilarTools/soundVisualizer} % Venstre billede
\end{minipage} \hfill
\begin{minipage}[b]{0.45\textwidth} \centering
\includegraphics[width=0.70\textwidth]{images/SimilarTools/soundVizz} % Højre billede
\end{minipage} \\ % Captions og labels
\begin{minipage}[t]{0.45\textwidth}
\caption{Sound Visualizer \cite{soundVisualizer}.} % Venstre caption og label
\label{fig:soundVisualizer}
\end{minipage} \hfill
\begin{minipage}[t]{0.45\textwidth}
\caption{SoundVizz \cite{soundVizz}.} % Højre caption og label
\label{fig:soundVizz}
\end{minipage}
\end{figure}

\begin{figure}[htbp]
\centering
\includegraphics[width=0.5\textwidth]{images/SimilarTools/audioTool}
\caption{Audio Tools \cite{audioTool}.}
\label{fig:audioTools}
\end{figure}

On the other hand there are sound generators such as \href{http://www.drpetter.se/project_sfxr.html}{sfxr} and \href{http://designthemedia.com/files/file/25-the-droner}{The Droner} which can generate sounds based on a wide range of parameters. However, these programs can be rather difficult to use and understand without any background knowledge. Seldom do the programs spent much time on visualizing and explaining what is going on behind the scenes. Instead, it is up to the user to figure out what each little knob does.

\begin{figure}[htbp] \centering
\begin{minipage}[b]{0.45\textwidth} \centering
\includegraphics[width=0.60\textwidth]{images/SimilarTools/sfxr} % Venstre billede
\end{minipage} \hfill
\begin{minipage}[b]{0.45\textwidth} \centering
\includegraphics[width=0.60\textwidth]{images/SimilarTools/droner} % Højre billede
\end{minipage} \\ % Captions og labels
\begin{minipage}[t]{0.45\textwidth}
\caption{\textit{sfxr} is used to generate simple 8-bit sounds \cite{sfxr}.} % Venstre caption og label
\label{fig:sfxr}
\end{minipage} \hfill
\begin{minipage}[t]{0.45\textwidth}
\caption{\textit{Droner} is used to generate sounds \cite{droner}.} % Højre caption og label
\label{fig:droner}
\end{minipage}
\end{figure}

\textit{TouchOSC}, which is a modular OSC and MIDI control surface for iPhone and iPad, is an example of how confusing it can be to use an interface if one doesn't know about all the buttons. It's hard to know even where to begin, especially since many of the buttons don't have labels.

\begin{figure}[htbp]
\centering
\includegraphics[width=0.5\textwidth]{images/SimilarTools/touchosc}
\caption{\textit{TouchOSC} is a modular OSC and MIDI control surface
 \cite{touchosc}.}
\label{fig:touchosc}
\end{figure}

There are plenty of different programs on the market, but most of them focus on either the training part or the visualization part. There seems to be a lack of software that attempts to combine the two aspects into a program with a focus on learning, as well as visualizing the sounds. Most visualization programs only use the visuals for aesthetically-pleasing means of illustrating sound, instead of using it for a practical purpose, such as teaching what and how a sound wave is being changed. It appears that many of the programs appeal to people who already feel confident working with audio; there are only few that aim to teach the topics at a beginner's level.

It was not possible to find a program that combines the different aspects together in an application that is easy and fun to use; visualizes sound in an intuitive manner; and gives the opportunity to really understand what is going on when sound is being manipulated by various filters.